This application claims the priority of German application 197 52 534.2, filed Nov. 27, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a radial-flow exhaust-gas turbocharger turbine having a row of adjustable guide blades which are rotatable via adjusting shafts mounted in a casing.
DE 43 09 636 A1 discloses a known type of exhaust-gas turbocharger turbine in which adjustable guide blades are provided to increase the turbine output, the turbine rotational speed and also the boost. The main purpose of such a turbine arranged in the exhaust-gas flow of an internal combustion engine is to drive a compressor, which feeds air, drawn in atmospherically and compressed therein, to the individual cylinders of the internal combustion engine via a boost-air line. A further purpose of such a turbine, however, is also its use during braking operation of an internal combustion engine.
For utilization during braking operation as a so-called turbobrake, the guide blades are completely closed by a corresponding rotation of their adjusting shafts. Here, however, so-called gap losses, which occur on account of unavoidable tolerances and an inevitably large clearance on account of the considerable temperature differences and changes in length resulting therefrom, are a problem.
In particular during braking operation of the exhaust-gas turbocharger turbine, there is a very large pressure difference between the regions upstream of the guide blades and downstream of the guide blades. A very high braking pressure prevails upstream of the guide blades, whereas virtually ambient pressure prevails downstream of the guide blades in the direction of the adjoining exhaust-gas system. The braking performance is therefore markedly reduced by the large gap losses. In addition, however, the relatively large gap cross-sections and small sealing areas lead to efficiency losses even during normal operation of the turbine.
Furthermore, with regard to the general prior art, reference is also made to DE 39 12 348 C2, DE 195 16 971 A1 and DE 39 07 504 C2.